U.S. patent number 7,217,588 [Application Number 11/178,148] was granted by the patent office on 2007-05-15 for integrated mems packaging.
This patent grant is currently assigned to Sharp Laboratories of America, Inc.. Invention is credited to Michael James Brownlow, John W. Hartzell, Harry Garth Walton.
United States Patent |
7,217,588 |
Hartzell , et al. |
May 15, 2007 |
Integrated MEMS packaging
Abstract
An integrated MEMS package and associated packaging method are
provided. The method includes: forming an electrical circuit,
electrically connected to the first substrate; integrating a MEMS
device on a first substrate region, electrically connected to the
first substrate; providing a second substrate overlying the first
substrate; and, forming a wall along the first region boundaries,
between the first and second substrate. In one aspect, the
electrical circuit is formed using thin-film processes; and,
wherein integrating the MEMS device on the first substrate region
includes forming the MEMS using thin-film processes, simultaneous
with the formation of the electrical device. Alternately, the MEMS
device is formed in a separate process, attached to the first
substrate, and electrical interconnections are formed to the first
substrate using thin-film processes.
Inventors: |
Hartzell; John W. (Camas,
WA), Walton; Harry Garth (Beckley, GB), Brownlow;
Michael James (Drayton, GB) |
Assignee: |
Sharp Laboratories of America,
Inc. (Camas, WA)
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Family
ID: |
36641020 |
Appl.
No.: |
11/178,148 |
Filed: |
July 8, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060148137 A1 |
Jul 6, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11031320 |
Jan 5, 2005 |
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Current U.S.
Class: |
438/51; 438/50;
438/48 |
Current CPC
Class: |
B81C
1/0023 (20130101); H01L 27/1214 (20130101) |
Current International
Class: |
H01L
21/00 (20060101) |
Field of
Search: |
;438/48-51,113-119
;257/730,777,569,678 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Le; Dung A.
Attorney, Agent or Firm: Law Office of Gerald Maliszewski
Maliszewski; Gerald
Parent Case Text
RELATED APPLICATIONS
This application is a continuation-in-part of a pending patent
application entitled, PIEZO-TFT CANTILEVER MEMS, invented by Zhan
et al., Ser. No. 11/031,320, filed Jan. 5, 2005. This application
is incorporated herein by reference.
Claims
We claim:
1. An integrated microelectromechanical system (MEMS) device
package, the MEMS integrated package comprising: a first substrate
having a first region with boundaries; an electrical circuit on a
second region of the first substrate, electrically connected to the
first substrate; a MEMS device environmental sensor on the first
region, electrically connected to the first substrate; a second
substrate overlying the first substrate, having an opening
overlying the first substrate first region, exposing the MEMS
device to a first environment via the second substrate opening;
and, a wall along the first region boundaries, between the first
and second substrates, isolating the MEMS device from the
electrical circuit.
2. The MEMS integrated package of claim 1 wherein the wall encloses
the MEMS device between the first and second substrates along the
first region boundaries.
3. The MEMS integrated package of claim 1 wherein the MEMS is a
micro-fluidic MEMS; and, wherein the second substrate opening
exposes the micro-fluidic MEMS to a fluid environment.
4. The MEMS integrated package of claim 1 wherein the electrical
circuit on the second region of the first substrate is an active
circuit including a TFT, electrically connected to the MEMS; and,
wherein the wall separates the TFT, exposed to a first environment,
from the MEMS, exposed to a second environment.
5. The MEMS integrated package of claim 1 wherein the wall is a
cured sealant.
6. The MEMS integrated package of claim 1 further comprising: a
plurality of uniform-shaped spacers applied to the first substrate;
and, wherein the wall is a cured sealant, with a uniform height
between the first and second substrates, response to the
spacers.
7. The MEMS integrated package of claim 1 wherein the first
substrate includes a plurality of regions with boundaries; the MEMS
integrated package further comprising: a plurality of MEMS devices
on the first substrate, each in a corresponding region; and, a
plurality of walls, each wall formed around the boundaries of a
corresponding region of the first substrate.
8. The MEMS integrated package of claim 1 further comprising: a
boundary assembly shape matching the first region boundaries, and
having a height; and, wherein the wall comprises the boundary
assembly attached to the first substrate along the first region
boundaries, separating the first substrate from the second
substrate by the boundary assembly height.
9. An integrated microelectromechanical system (MEMS) device
package, the MEMS integrated package comprising: a liquid crystal
display (LCD) substrate having a perimeter and a first region with
boundaries; an electrical circuit on a second region of the first
substrate, electrically connected to the first substrate; a MEMS
device on the first region, electrically connected to the first
substrate; a color filter substrate overlying the LCD substrate;
and, a seal formed along the perimeters of the display substrate
and color filter substrate; and, a cavity between the display
substrate and the color filter substrate, bounded by the seal.
10. The MEMS integrated package of claim 9 further comprising:
liquid crystal material in the cavity.
11. The MEMS integrated package of claim 9 wherein the color filter
substrate has an opening through the substrate, overlying the first
substrate first region; wherein the MEMS device is a MEMS
microphone.
12. The MEMS integrated package of claim 9 wherein the seal
encloses the MEMS device between the LCD and color filter
substrates along the first region boundaries.
13. The MEMS integrated package of claim 9 wherein the seal
hermetically seals the MEMS device between the LCD and color filter
substrates along the first region boundaries.
14. The MEMS integrated package of claim 9 wherein the MEMS device
is selected from the group including an acoustic speaker, a
microphone, a radio frequency (RF) filter, an RF antenna, an
accelerometer, a gyroscope, a chemical sensor, a temperature
sensor, a humidity sensor, a pressure sensor, a light sensor, an
infrared sensor, and an actuator.
15. An integrated microelectromechanical system (MEMS) device
package, the MEMS integrated package comprising: a first substrate
having a first region and a groove formed along first region
boundaries; an electrical circuit on a second region of the first
substrate, electrically connected to the first substrate; a MEMS
device on the first region, electrically connected to the first
substrate; a second substrate overlying the first substrate, with a
groove formed in a region opposite the groove in the first
substrate; and, a wall formed from an O-ring seated in the first
and second substrate grooves.
16. The MEMS integrated package of claim 15 wherein the O-ring wall
encloses the MEMS device between the first and second substrates
along the first region boundaries.
17. The MEMS integrated package of claim 16 wherein the O-ring wall
hermetically seals the MEMS device between the first and second
substrates along the first region boundaries.
18. The MEMS integrated package of claim 15 wherein the MEMS device
is selected from the group including an acoustic speaker, a
microphone, a radio frequency (RF) filter, an RF antenna, an
accelerometer, a gyroscope, a chemical sensor, a temperature
sensor, a humidity sensor, a pressure sensor, a light sensor, an
infrared sensor, and an actuator.
19. The MEMS integrated package of claim 15 wherein the second
substrate has an opening overlying the first substrate first
region, exposing the MEMS device to a first environment via the
second substrate opening; and wherein the O-ring wall isolates the
MEMS device from the electrical circuit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to the packaging of
microelectromechanical systems (MEMS) and, more particularly, to a
system and method for simultaneously packaging a MEMS device with
active circuitry on an integrated circuit (IC) substrate.
2. Description of the Related Art
MEMS devices are typically made on silicon wafers; using one of two
well established techniques: bulk micro-machining or surface
micro-machining. In both of these methods, the MEMS device is
fabricated on a silicon wafer using standard IC-type fabrication
equipment. Once the wafer is processed, the wafer is diced to form
individual die. These MEMS die may or may not be integrated with
electronic components (on CMOS). Once the die is cingulated, it
must then be packaged in some form of package, similar to an IC
package. This package is eventually inserted into a socket or
bonded to a Printed Circuit Board (PCB) as part of an overall
system, i.e., a cell phone. These packages can be quite elaborate,
depending on the MEMS style and application, including vacuum
package requirements. In addition, because many MEMS devices are
required to move during operation, the package must provide a
cavity that allows for this movement.
One problem with this type of MEMS packaging methodology is that
the package is a very large proportion of the total MEMS device
cost; on the order of 30 70% of the overall cost. This packaging
cost can, therefore, have a significant impact on the capability of
such MEMS devices to penetrate cost-sensitive markets, such as the
cell phone market.
Another problem with existing MEMS packaging is the noise inherent
with the electrical connections between the MEMS package and the
rest of the system. The bonding, wiring, and electrical
interconnections associated with interfacing a MEMS device embedded
in a package, to a circuit, necessarily adds impedance mismatches
that result in noisy or low amplitude signals.
However, there is mounting evidence that MEMS technology can add
value to systems, such as cell phones, in a market that is ripe for
new technology, if only the packaging issue could be addressed.
Continuing with the cell phone example, it is certain that the
camera-on-cell phone has made a great impact on the market. The
search is on for the next added functionality that can drive new
expansion of the cell phone market.
MEMS are being considered for the following cell phone
functions:
1) Motion capture (Accelerometer and gyroscope);
2) Microphones;
3) RF devices and RF modules;
4) Image capture;
5) Low power solutions;
6) Identification (biometrics);
7) Enhanced display functionality; and,
8) Personal health and safety monitoring.
The issues preventing MEMS penetration into the cell phone market
are cost and performance. As mentioned above, packaging is 30 70%
of the MEMS device cost. This cost issue is preventing the
integration of MEMS into cell phones, display systems, and many
other types of electronic devices.
MEMS devices are a logical derivative of semiconductor IC processes
that may be used to develop micrometer scale structural devices
such as transducers or actuators, and they are typically fabricated
on silicon substrates. MEMS devices typically interface physical
variables and electronic signal circuits. The integration of MEMS
into larger scale systems has been expensive to fabricate due to
the process difficulties and the cost associated with integrating
the MEMS standard IC technologies, such as CMOS. The processes used
to fabricate MEMS on glass offer the advantage that the integration
of electrical and mechanical functions is easily done. In this way,
system level integration is possible and cost effective.
It would be advantageous if MEMS devices could be packaged as part
of the overall process of fabricating active devices on a circuit
board or display.
SUMMARY OF THE INVENTION
The problem solved by this invention is the creation of a low-cost
packaging system for the integration of electrical, mechanical and
optical MEMS devices with electrical systems. By way of example,
the packaging of MEMS device on a display screen is presented
(i.e., a cell phone display), but the invention is not limited to
any particular electrical system. Generally, it is assumed that the
MEMS device to be packaged can be any type of mechanical,
electrical, optical, or micro-fluidic device that requires
encapsulation or packaging.
One aspect of this invention deals with the integration of MEMS on
glass substrates using low temperature polysilicon technology.
Using this invention, the MEMS device and amplification circuitry
can be integrated together, monolithically fabricated on the glass
substrate and encapsulated. The advantage of monolithic fabrication
is the seamless blending of electrical and mechanical devices in
the polysilicon integrated approach resulting in overall system
electrical quality better than, or similar to the approach where
discreet MEMS packages are integrated with standard integrated
circuits.
Accordingly, a method is provided for packaging a MEMS device. The
method comprises: forming an electrical circuit electrically
connected to a first substrate; integrating a MEMS device on a
first substrate region, electrically connected to the first
substrate; providing a second substrate overlying the first
substrate; and, forming a wall along the first region boundaries,
between the first and second substrates.
In one aspect, the electrical circuit is formed using thin-film
processes; and, integrating the MEMS device on the first substrate
region includes forming the MEMS using thin-film processes,
simultaneous with the formation of the electrical device.
Alternately, the MEMS device is formed in a separate process,
attached to the first substrate, and electrical interconnections
are formed to the first substrate using thin-film processes.
The wall formed along the first region boundaries may act to
enclose the MEMS device between the first and second substrates.
For example, the MEMS device may be hermetically sealed.
Alternately, the second substrate may have an opening through it,
and the MEMS device may be an environmental sensor. The wall
between the first and second substrate then acts to isolate the
MEMS device from the electrical circuit, while exposing the MEMS
device to an environment via the second substrate opening. For
example, the MEMS environmental sensor may be a micro-fluidic MEMS
that is exposed to a fluid environment.
The wall between the first and second substrate may be a sealant
bonding the first substrate to the second substrate. Spacers may be
used to maintain a uniform distance between the first and second
substrates. In another aspect, the wall is an O-ring held in place
by grooves in the first and second substrates.
Additional details of the above-described method and an integrated
MEMS device package are provided below.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B is a partial cross-sectional and plan views,
respectively, of an integrated microelectromechanical system (MEMS)
device package.
FIG. 2 is a plan view showing an alternate configuration of the
wall separating the MEMS from the electrical circuit.
FIG. 3 is a perspective drawing showing a wall formed as part of a
prefabricated separating assembly.
FIG. 4 is a cross-sectional view depicting a first alternate aspect
of the integrated package of FIG. 1B.
FIG. 5 is a cross-sectional view depicting a second alternate
aspect of the integrated package of FIG. 1B.
FIG. 6 is a partial cross-sectional view of a variation in the
integrated package of FIG. 1B.
FIGS. 7A and 7B are partial cross-sectional and plan views,
respectively, of a liquid crystal display (LCD) integrated
package.
FIGS. 8A and 8B are partial cross-sectional and plan views,
respectively, of an alternate aspect of the integrated package of
FIGS. 1A and 1B.
FIG. 9 is a partial cross-sectional view showing an alternative
wall design.
FIGS. 10A and 10B are plan and partial cross-sectional views,
respectively, depicting the encapsulation of a MEMS device on a
display substrate.
FIG. 11 is a flowchart illustrating a method for packaging a MEMS
device.
DETAILED DESCRIPTION
FIGS. 1A and 1B is a partial cross-sectional and plan views,
respectively, of an integrated microelectromechanical system (MEMS)
device package. The MEMS integrated package 100 comprises a first
substrate 102 having a first region 104 with boundaries 106. An
electrical circuit 108 is formed on a second region 110 of the
first substrate 102. The electrical circuit 108 is electrically
connected to the first substrate 102. For example, traces in the
first substrate may conduct dc power, ground, and electrical
signals to the electrical circuit 108. A MEMS device 112 is shown
on the first region 104, electrically connected to the first
substrate 102. The boundaries 105 may, or may not completely form a
perimeter that surrounds the MEMS device 112. A second substrate
114 overlies the first substrate 102. A wall 116 is formed along
the first region boundaries 106, between the first substrate 102
and second substrate 114.
In its simplest form, the first substrate 102 is a one-sided board
with electrical traces on one of the surfaces. In this case, the
electrical circuit 108 and the MEMS 112 may be dice that are
attached using ball grid array (BGA) connections, or electrically
connected using thin-film processes such as metal deposition and
selective etching. Typically however, the first substrate is made
from multiple electrical layers separated by interlevel
dielectrics, as is common in CMOS and thin-film processes.
Low-temperature thin-film processes are often used if the first
substrate is glass, plastic, or quartz, as would be the case if a
liquid crystal display (LCD) is being fabricated. As shown, the
MEMS 112 is connected through via 118 and interlevel trace 120 to
the electrical circuit 108.
In some aspects, the electrical interconnection between the MEMS
112 and the electrical circuit 108 may carry an electrical signal.
For example, the MEMS 112 may trigger the gate of a TFT electrical
circuit. In other aspects, the MEMS 112 and the electrical circuit
108 merely share common dc voltages and grounds (the MEMS does not
electrically communicate with the electrical circuit). In another
aspect, the MEMS 112 may be electrically connected to other circuit
boards via a connector to the first substrate 102 (not shown). For
example, the MEMS device 112 may a microphone mounted on the LCD
screen of a cell phone, in communication with the cell phone
transmission circuitry.
FIG. 2 is a plan view showing an alternate configuration of the
wall separating the MEMS from the electrical circuit. The wall 116
may completely enclose the MEMS 112, with the first substrate 102,
the second substrate 114, along the first region boundaries 106, as
shown in FIG. 1B. That is, the combination of substrates and wall
form a cavity in which the MEMS 112 is seated. In one aspect, the
wall hermetically seals the MEMS device 112 between the first
substrate 102 and second substrate 114 along the first region
boundaries 106. Alternately as shown in FIG. 2, the MEMS 112 is
separated from the electrical circuit because the electrical
circuit 108 is completely enclosed by wall 116. Such an integrated
package acts to generally protect the MEMS 112 while exposing it to
the ambient environment. The wall 116 may hermetically seal the
electrical circuit 108.
FIG. 4 is a cross-sectional view depicting a first alternate aspect
of the integrated package of FIG. 1B. The second substrate 114 has
a third region 400 with an opening 402, overlying the first
substrate first region 104. The opening 402 exposes the MEMS device
112 to an environment. For example, the MEMS 112 may be an
environmental sensor. The wall 116 isolates the MEMS device 112
from the electrical circuit 108 along the first region boundaries
106. It may be undesirable that the electrical circuit is exposed
to the environment seen by the MEMS. For example, the MEMS 112 may
be microphone exposed to the ambient environment via opening
402.
FIG. 5 is a cross-sectional view depicting a second alternate
aspect of the integrated package of FIG. 1B. Here, the MEMS 112 is
a micro-fluidic MEMS, depicted as a piezo-TFT cantilever. The
second substrate opening 402 exposes the micro-fluidic MEMS to a
fluid environment. The integrated package 100 may be immersed in a
fluid, or as shown, the fluid is introduced to the opening 402
through a tube 500.
As shown, the electrical circuit 108 on the second region 110 of
the first substrate 102 is an active circuit including a TFT,
electrically connected to the MEMS 112 via a trace 504. The wall
116 along the first region boundaries 106 separates the TFT 108,
exposed to a first environment, from the MEMS 112, exposed to a
second environment. For example, the first environment can be
ambient atmosphere and the second environment can be a fluid. As
shown, in some aspects the wall 116 is a cured sealant.
FIG. 6 is a partial cross-sectional view of a variation in the
integrated package of FIG. 1B. In some aspects, the wall 116
includes uniformly-sized spacers 600 embedded in a cured sealant
602, to maintain a uniform distance 604 between the first substrate
102 and the second substrate 114. Alternately, as shown in FIG.
10B, a plurality of uniform-shaped spacers applied to the first (or
second) substrate 102. The wall is a cured sealant 602, with a
uniform height 604 between the first and second substrates,
response to the spacers 600.
FIGS. 7A and 7B are partial cross-sectional and plan views,
respectively, of a liquid crystal display (LCD) integrated package.
FIG. 7A is not exactly drawn to the scale of FIG. 7B. The first
substrate 102 is an LCD display substrate (i.e., glass) with a
perimeter 700. As in FIG. 1B, the MEMS 112 is enclosed by wall 116.
The second substrate 114 is a color filter substrate with a
perimeter 702. Perimeter 700 cannot be seen in FIG. 7B, but is
approximately underlies perimeter 702 (substrate 102 cannot be seen
in the plan view). A seal 704 is formed along the perimeters
700/702 of the display substrate 102 and color filter substrate
114. A cavity 706 is formed between the display substrate 102 and
the color filter substrate 114, bounded by the seal 704. In one
aspect, the cavity 706 is filled with liquid crystal material. In
this case, the wall prevents the liquid crystal material from
coming in contact with the MEMS 112.
In one aspect as shown, the color filter substrate 114 has a third
region 708 with an opening 710 through the substrate, overlying the
first substrate first region 104. For example, the MEMS device 112
can be a MEMS microphone. However, other types of MEMS devices can
be package integrated into an LCD.
FIGS. 8A and 8B are partial cross-sectional and plan views,
respectively, of an alternate aspect of the integrated package of
FIGS. 1A and 1B. The first substrate 102 includes a plurality of
regions with boundaries. Shown are regions 800, 802, and 804, with
respective boundaries 806, 808, and 810. The MEMS integrated
package 100 further comprises a plurality of MEMS devices 812, 814,
and 816 on the first substrate 102, each in a corresponding region.
A plurality of walls 818, 820, and 822 are formed around the
boundaries of a corresponding region of the first substrate. FIG. 9
is a partial cross-sectional view showing an alternative wall
design. The first substrate 102 includes a groove 900 formed along
the first region boundaries 106. Likewise, the second substrate 114
includes a groove 902 formed in a region opposite the groove 900 in
the first substrate 102. In this case the wall 116 is an O-ring
seated in the first and second substrate grooves 900/902. This
arrangement permits a seal to be formed by merely clamping the
substrates 102/114 together. Although only sealant and O-ring walls
have been specifically depicted, the integrated package is not
limited to any particular wall design. In some aspects not shown,
the wall is formed by the deposition and selective etching of field
oxide. Alternately, the wall can be formed in conventional LC
display substrate fabrication processes.
FIG. 3 is a perspective drawing showing a wall formed as part of a
prefabricated separating assembly. A boundary assembly 300 is shown
having the shape matching the first regions boundaries 106, and
having a height 302. Note, the assembly can be made from separate
pieces that may, or may not interlock. The assembly pieces can be a
conventional rigid, semi-rigid, or even flexible plastic material.
In this aspect, the wall 116 comprises the boundary assembly 300
attached to the first substrate 102 along the first region
boundaries 106, separating the first substrate 102 from the second
substrate (not shown for clarity) by the boundary assembly height
302. The boundary assembly can be fixed in place by an adhesive or
held in place by substrate friction.
Although only microphone and fluidic MEMS devices have been
specifically depicted, the present invention integrated package is
not particularly limited to any type of MEMS or MEMS function. For
example, other MEMS that can be packaged include an acoustic
speaker, a radio frequency (RF) filter, an RF antenna, an
accelerometer, a gyroscope, a chemical sensor, a temperature
sensor, a humidity sensor, a pressure sensor, a light sensor, an
infrared sensor, or an actuator.
Functional Description
Conventionally, MEMS on display are packaged as discreet components
in IC-like packages and then attached to the system using standard
IC packaging assembly techniques. This invention teaches a new way
to establish the MEMS package on the display itself, by utilizing
the existing display assembly process to create the package,
resulting in a no-cost package for the MEMS device. Given the high
cost of typical MEMS packages, this invention has a clear advantage
for display integration and system level cost reduction.
FIGS. 10A and 10B are plan and partial cross-sectional views,
respectively, depicting the encapsulation of a MEMS device on a
display substrate. Note, the MEMS device area (D3) is not to scale
in FIG. 10B. The actual device area is much smaller, so as to not
interfere with the display operation. The invention creates a MEMS
(or other device) encapsulation/package on a display substrate by
using the standard cell processing in the LCD manufacturing
process. The MEMS can be either monolithically fabricated on the
display substrate during the array process, or transferred after
the array process is complete. The MEMS devices are encapsulated
during the display cell process, with display substrates on the top
and bottom and sealant (bounding the glass substrates together on
the sides). Referencing FIGS. 10A and 10B, an exemplary fabrication
process follows.
1) A MEMS device (or other mechanical, electrical or optical
device) is attached to a display substrate (S1), either through
monolithic fabrication of the MEMS device during array fabrication
or transfer of the device to S1 after array fabrication.
2) A counter substrate (S2) (color filter substrate in the case of
many LCD display processes) is prepared for mating to the first
substrate (S1), to form a display device. Prior to bonding S1 and
S2, spacers are applied to one of the substrates to maintain even
separation between S1 and S2 after bonding. This is a standard LCD
cell process.
3) A sealant is applied to either S1 or S2, forming the outline of
at least one display area and at least one separate area for
devices (D3), such as MEMS.
4) S1 and S2 are bonded together forming a display device and an
encapsulated package for the devices area (D3), bounded on the
sides by the sealant and the top and bottom by S1 and S2.
5) The display area likely undergoes further processing, such as
injection of liquid crystal material (in the case of LCD display).
However, D3 can be protected from these additional processes by the
encapsulation.
6) D3 can possibly be a vacuum package, depending on the processing
steps and environment of the processes that bond S1 and S2.
7) If it is desirable to expose device area D3 to the environment,
then one or both S1 and S2 may be pre-drilled in the area of D3 to
provide this condition. This is desirable in the case where D3
houses an environmental sensor, for example.
8) Because the device area (D3) and the display area are separately
encapsulated, there is no cross contamination.
Another aspect of the invention uses the encapsulation method for
the integration of devices (such as MEMS) through some sort of
transfer process. For example, in the case of amorphous silicon
displays, the MEMS device might be fabricated on another substrate
and later transferred to the display substrate. Subsequent to this
transfer there are additional process steps to integrate the
electrical and mechanical devices, followed by the final
encapsulation process. Although LCD displays have been used as an
example, in other aspects the present invention packaging technique
can also be used OLED, electrophoretic, FED, and other types of
displays.
In a different aspect, multiple device areas can be created using
the above-mentioned techniques to accomplish one of the
following:
1) Packaging areas can be separated by functionality. For example,
one packaged device area can be a vacuum package, containing MEMS
devices requiring a vacuum environment, and another is exposed to
the environment (containing environment sensors), through holes
drilled in one of the glass substrates.
2) Packaging areas can be separated by a defined distance, but
linked by operation. For example, a first device area might contain
a MEMS microphone. A second, separate, device area might contain a
second MEMS microphone. Because the exact spatial relationship
between the devices is controlled within the stringent limits of a
photolithography process, the two devices can be coupled into a
system solution. In the case of microphone example, the acoustic
input can be coupled and the known microphone spatial relationship
used to sense from where a particular sound is coming. The sound
source data can be used to accomplish some desired result.
MEMS on Glass
The use of glass substrates offers unique opportunities to produce
surface novel micro machined devices and integrate them into system
level applications. Table 1 highlights some of the advantages of
MEMS on glass over MEMS on silicon substrates.
TABLE-US-00001 TABLE 1 Comparison of Silicon vs. Glass substrates
Silicon Attribute substrate Glass substrate Cost moderate low Max
substrate size (m.sup.2) 1 >2.7 Optical properties Transparent
to Transparent to all IR wavelengths Electrical insulation poor
excellent Dielectric properties poor excellent Biological
compatibility poor excellent Thermal insulation poor excellent Max
temperature 1400 C. 650 C. Crystallographic bulk yes no etch
MEMS on glass offer the following unique points:
1) The optical transparency of glass (other than its obvious
advantage for displays) permits the creation of novel MEMS devices.
For example, it is possible to optically sense the motion of a
device through the substrate without requiring through-holes or
expensive packaging.
2) MEMS devices can be built on the same substrate as LC displays.
This provides opportunities to build other novel devices, such as
integrated MEMS sensors on display.
3) Integrated RF on display One of the stumbling blocks when
developing RF and electromagnetic MEMS devices is the effect of the
silicon substrate. Typically, large quantities of substrate must be
removed to improve the quality of the MEMS device. By using a glass
substrate, this process is not necessary and the devices are
simpler to manufacture and are more physically robust (since the
substrate is intact).
4) Additionally, many MEMS processes need to take special steps to
electrically isolate individual moving elements from each other
when they're all attached to the same conductive and parasitic
substrate. Again, with glass, this isolation is inherently not
necessary.
5) Micro-fluidic and biological applications often require
materials that are bio-compatible, i.e. are biologically inert.
Glass is one such material. It is simpler to start with a
bio-compatible material (such as a glass substrate) than to use
incompatible materials and coat them with appropriate surfaces.
6) Quite a few MEMS applications require thermal insulation between
elements, such as bio-meters (IR sensors), field emission tips, and
chemical detectors. With devices on a silicon substrate, much of
the substrate must be removed to provide this thermal insulation.
By using a glass substrate, each element is inherently
isolated.
FIG. 11 is a flowchart illustrating a method for packaging a MEMS
device. Although the method is depicted as a sequence of numbered
steps for clarity, the numbering does not necessarily dictate the
order of the steps. It should be understood that some of these
steps may be skipped, performed in parallel, or performed without
the requirement of maintaining a strict order of sequence. Various
steps in the method may be better understood in the context of the
explanations of FIGS. 1A through 10B, above. The method starts at
Step 1100.
Step 1102 provides a first substrate having a first region with
boundaries. Step 1104 forms an electrical circuit on a second
region of the first substrate, electrically connected to the first
substrate. Step 1106 integrates a MEMS device on the first region,
electrically connected to the first substrate. Some examples of
MEMS devices include an acoustic speaker, a microphone, a radio
frequency (RF) filter, an RF antenna, an accelerometer, a
gyroscope, a chemical sensor, a temperature sensor, a humidity
sensor, a pressure sensor, a light sensor, an infrared sensor, and
an actuator. Step 1108 provides a second substrate overlying the
first substrate. Step 1110 forms a wall along the first region
boundaries, between the first and second substrate.
In one aspect, forming the electrical circuit in Step 1104 includes
forming an electrical device using thin-film processes. Step 1106
integrates the MEMS device on the first region using thin-film
processes, simultaneous with the formation of the electrical
device. Alternately, integrating the MEMS device on the first
region in Step 1106 includes substeps (not shown). Step 1106a forms
the MEMS device (i.e., in a process independent of the electrical
circuit (Step 1104). Step 1106b attaches the MEMS device to the
first substrate first region. Step 1106c forms electrical
interconnections between the MEMS device and the first substrate
using thin-film processes.
In one aspect, forming a wall along the first region boundaries in
Step 1110 includes enclosing the MEMS device between the first
substrate, the second substrate, and the wall. For example, the
MEMS device can be hermetically enclosed.
In a different aspect, Step 1108 provides a second substrate having
an opening overlying the first substrate first region. In this
aspect, Step 1106 integrates a MEMS environmental sensor. Step 1110
forms a wall along the first region boundaries using the following
substeps (not shown). Step 1110a isolates the MEMS device from the
electrical circuit, and Step 1110b exposes the MEMS device to a
first environment via the second substrate opening. For example,
Step 1106 may integrate a micro-fluidic MEMS, and Step 1110b
exposes the micro-fluidic MEMS to a fluid environment.
In another example, Step 1104 forms an active circuit including a
TFT, electrically connected to the MEMS. Then, forming a wall
between the first and second substrate along the first region
boundaries in Step 1110 includes alternate substeps (not shown).
Step 1110c exposes the MEMS to a first environment. Step 1110d
exposes the TFT to a second environment.
In another aspect, Step 1110 forms a wall along the first region
boundaries using the following substeps. Step 1110e applies a
sealant along the first region boundaries, and Step 1110f bonds the
first substrate to the second substrate. In one variation, Step
1110g applies uniformly shaped spacers to the first substrate and
Step 1110h maintains a uniform distance between the first and
second substrates in response to the spacers. Alternately, forming
a wall in Step 1110 includes other substeps. Step 1110i forms a
groove in the first substrate along the first region boundaries,
and Step 1110j forms a groove in the second substrate, opposite the
groove in the first substrate. Then, Step 1110k seats an O-ring in
the first and second substrate grooves. Note, the grooves may also
be preformed in the substrates that are provided in Step 1102 and
1108.
In one specific example, Step 1102 provides a liquid crystal
display (LCD) display substrate with a perimeter, and Step 1108
provides a color filter substrate with a perimeter. Then, Step 1112
seals the display substrate to the color filter substrate along the
perimeters to form a cavity. Step 1114 fills the cavity with a
liquid crystal material. In one variation of this example, Step
1108 provides a color filter substrate having an opening through
the substrate, overlying the first substrate first region, and Step
integrates a MEMS microphone.
In another aspect, Step 1102 provides a first substrate with a
plurality of regions with boundaries, and Step 1106 integrates a
plurality of MEMS devices on the first substrate, each in a
corresponding region. Then, Step 1110 forms a wall around the
boundaries of each region of the first substrate.
In another aspect, forming a wall along the first region boundaries
in Step 1110 includes: providing a boundary assembly having a shape
matching the first region boundaries and a height; and, attaching
the boundary assembly to the first substrate, overlying the first
region boundaries, separating the first substrate from the second
substrate by the boundary assembly height.
An integrated MEMS package and MEMS packaging method have been
provided. Examples of particular MEMS devices and electrical
circuits have been given to help illustrate the invention. However,
the invention is not limited to merely these examples. Other
variations and embodiments of the invention will occur to those
skilled in the art.
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